For the SAE Mini Baja project I decided it would be cool to have a tachometer for the driver to view how fast the car was moving and it's top speed. 

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To measure the speed of the vehicle a Hall effect sensor was used to measure the RPM of the rear wheel axle with a magnet glued to it. The magnet is necessary for the sensor to work. This value was then converted to velocity based on the wheel's diameter. This measurement assumes no wheel slip.

 

To process this data an Arduino mega was used. This data was then displayed on a TFT display. 

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The enclosure was 3D-Printed and then coated in latex primer to give a smooth surface. The enclosure was made on short notice as it wasn't given the OK to be used till a few days before competition. 

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It worked very well up until competition where the LIPO battery failed due to one of the cells coming unbalanced during it's charge.